Magic Resistance. The Skeleton Dragon has advantage on saving throws against spells and other magical effects.

Summon Flameskulls The Skeleton Dragon can twice per encounter summon 2d4 Flameskulls, once he's at 100hp and once when he's at 50hp.

Flameskulls summoned this way only have 20Hp, and they don't have the Rejuvenation and the Spellcasting traits

Multiattack. The Skeleton dragon makes two attacks: one with its bite and one with its claws.

Bite. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing damage.

Claw. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) slashing damage.

Breath Weapons (Recharge 5–6). The Skeleton dragon uses one of the following breath weapons.

Cold Breath. The Skeleton dragon exhales an icy blast in a 30-foot cone. Each creature in that area must make a DC 15 Constitution saving throw, taking 8d8 cold damage on a failed save, or half as much damage on a successful one.

Frightful Presence. Each creature of the Skeleton Dragon choice that is within 120 feet of the dracolich and aware of it must succeed on a DC 15 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature’s saving throw is successful or the effect ends for it, the creature is immune to the dracolich’s Frightful Presence for the next 24 hours.